This study will investigate whether administration of the anti-retroviral agent zidovudine (ZDV) can reduce the vertical transmission rate of HIV infection. ZDV will be administered orally to HIV-infected pregnant women at 14 to 34 weeks gestation and an intrapartum I.V. dose will be given to the mother, oral doses will be given to their newborn infants from birth to six weeks of age. (ACTG 076)